1. Field of the Invention
This invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, this invention relates to a design for a simplified wafer level camera module that can be reflow soldered to a hosting device.
2. Description of the Background Art
Digital camera modules are currently being incorporated into a variety of host devices. Such host devices include cellular telephones, personal data assistants (PDAs), computers, etc. Therefore, consumer demand for digital camera modules in host devices continues to grow.
Host device manufacturers prefer digital camera modules to be small, so that they can be incorporated into the host device without increasing the overall size of the host device. Further, host device manufacturers prefer camera modules that minimally affect host device design. In meeting these requirements the host device manufacturers prefer camera modules that capture images of the highest possible quality. Of course, it is an ongoing goal for camera module manufacturers to design camera modules that meet these requirements at minimal manufacturing cost.
A conventional digital camera module generally includes a lens assembly, a housing, a printed circuit board (PCB), and an integrated image capture device (ICD). Typically, the components are formed separately and later assembled to create the digital camera module. That is, the ICD is attached to the PCB, and then the housing is attached to the PCB so that the ICD is covered by the bottom of the housing. Then, the lens assembly is mounted to the opposite end of the housing to focus incident light onto an image capture surface of the ICD. Typically, the lens assembly includes a sloped surface (e.g., threads, cam, ramps, etc.) that engage a complementary sloped surface formed on the housing such that proper focusing can be achieved by rotating the lens assembly within the housing. After the lens assembly is properly displaced with respect to the image capture surface, the lens assembly is fixed (e.g., via adhesive, thermal weld, etc.) with respect to the housing. The ICD is electrically coupled to the PCB, which includes a plurality of electrical contacts for the ICD to communicate image data to the host device for processing, display, and storage.
In manufacturing these camera modules, many problems are encountered by the camera module manufacturers. As an example, bare ICD dies are extremely vulnerable to contamination when exposed to contaminants such as dust and/or other particulate debris. Further, ICDs are extremely vulnerable when exposed to materials (e.g., adhesives) and processes (e.g., housing attachment, molding, lens attachment, etc.) used in the assembly of the camera modules. Contamination typically results in the discarding of the defective image capture devices which can be extremely expensive, especially when yield losses are high. To minimize contamination, the camera modules are typically assembled in class 100 clean rooms. Although the image capture devices of assembled camera modules are protected from contaminants outside of the camera module, they are still vulnerable to internal contaminants. Such internal contaminants are usually the result of trapped dust, adhesives, and/or particulates formed by frictional wear within the camera module. Frictional wear typically occurs during assembly processes such as focusing. In particular, particles are formed when the sloped surface of the lens assembly rubs against the sloped surface of the housing. Contamination of an image sensor after the camera is assembled can be especially expensive because the entire camera module may have to be discarded.
Another challenge faced by camera module manufacturers is that the components of camera modules are extremely small and, therefore, require extremely delicate, and therefore, expensive processes for fabrication, assembly, and alignment. Indeed, the alignment process becomes increasingly more difficult as the number of required camera module components is increased. This is because the strict position tolerances between camera module components accumulate proportionally with the number of components coupling the image capture surface to the lenses. Ideally, the lenses should all be coaxially perpendicular to the center of the planar image capture surface. However, this is typically only achieved within a predetermined overall tolerance defined by the sum of: the tolerance of the ICD with respect to the PCB, the tolerance of the PCB with respect to the housing, the tolerance of the housing with respect to the focus/zoom device, and the tolerances of the lenses with respect to the focus/zoom device.
As yet another example problem, camera modules typically cannot be reflow soldered to host devices without damaging the camera module. Reflow soldering is a very well developed and efficient electronic manufacturing process. Therefore, it would be desirable to be able to use a reflow solder process to attach camera modules to host devices. However, known devices cannot withstand reflow solder attachment.
What is needed, therefore, is a camera module that is less vulnerable to contamination of the image capture surface. What is also needed is a camera module that can be assembled with a more forgiving tolerance between the lenses and the image capture surface. What is also needed is a camera module that requires fewer components and fewer manufacturing steps. What is also needed is a camera module that can withstand a reflow soldering process.